1. Field of the Invention
The present invention relates to systems and methods for protecting vehicle occupants from injury. More specifically, the present invention relates to inflators designed to provide variable quantities of inflation gas at varying temperatures through variation of an activation signal used to trigger deployment of the inflator.
2. Description of Related Art
The inclusion of inflatable safety restraint devices, or airbags, is now a legal requirement for many new vehicles. Airbags are typically installed in the steering wheel and in the dashboard on the passenger side of a car. In the event of an accident, an accelerometer within the vehicle measures the abnormal deceleration and triggers the expulsion of rapidly expanding gases from an inflator. The expanding gases fill the airbags, which immediately inflate in front of the driver and passenger to protect them from impact against the windshield.
Side impact airbags such as inflatable curtains and seat mounted airbags have also been developed in response to the need for protection from impacts in a lateral direction, or against the side of the vehicle. Other airbags such as knee bolsters and overhead airbags also operate to protect various parts of the body from collision.
Known inflators generally fall into three categories: pyrotechnic inflators, compressed gas inflators, and hybrid inflators. Pyrotechnic inflators depend solely on combustion to provide inflation gas, while compressed gas inflators may use only a minimal amount of pyrotechnic that opens a chamber to release the inflation gas from a compressed state. Hybrid inflators use a combination of combustion and compressed gas storage to provide the inflation gas to fill the cushion.
Of all of the types described above, most inflators have the capacity to produce only a certain, pre-established quantity of inflation gas. The quantity and rate of gas production determine how hard the cushion will be upon inflation. Softer cushions are beneficial in low velocity collisions, in which the cushion need not be extremely stiff to prevent the occupant from contacting the vehicle interior. However, for high speed collisions, a stiffer cushion is needed to more rapidly absorb the occupant's momentum. Other factors such as the occupant's weight and position influence the optimal stiffness of the cushion.
Since all of the above factors can be expected to vary for any single collision situation, it would be desirable to create an inflator capable of providing varying quantities of inflation gas at varying temperatures in response to changes in vehicle velocity, occupant weight, occupant position, and the like. The desirability of such a system is reflected in the United States government's new frontal safety requirements, as set forth in the FMVSS 208 Ruling.
In response to this need, variable output, or “adaptive” inflators have been created. Adaptive inflators often have multiple chambers, each of which has an initiator. The initiators are independently controllable so that fewer chambers are opened for a low speed collision, while more chambers are opened to provide more inflation gas under high speed impact conditions. Unfortunately, many such designs are quite expensive. The use of multiple chambers, initiators, and the like adds significantly to the cost of the parts and assembly of the inflator. In general, the need for pyrotechnic initiators, ignition materials, gas generants, and the like adds significantly to the cost of known inflators.
Furthermore, known adaptive inflators are typically able to produce gas only at a limited number of discrete quantities. For example, an adaptive inflator may only be capable of producing a small quantity of inflation gas for a low speed collision or a large quantity of inflation gas for a high speed collision. If a medium speed collision occurs, the inflator may have to revert to the setting for high speed impact, thereby providing a cushion that is harder than necessary, and thus more likely to cause minor injury.
Accordingly, a need exists for an airbag inflation apparatus and method that are capable of producing a comparatively finely tunable quantity of inflation gas at varying temperatures. A need further exists for such an apparatus and method that can be utilized with a minimum number of parts that require a comparatively small amount of time and resources to assemble to reduce the overall cost of the airbag module. Furthermore, a need exists for such an apparatus and method that is adaptable to suit multiple cushion types and inflation gas distribution schemes.